In recent years, various wireless communication devices such as WLAN (Wireless Local Area Network) have been installed in apparatuses such as a personal computer, a peripheral device, a mobile telephone, a game machine, and home electronics. Among them, in a mobile apparatus such as a note type personal computer, the mobile telephone, and the game machine, there is a case that a user moves while executing an application. For example, a situation in which the user moves while making a call by using the mobile telephone can be easily imagined.
When the user moves while performing wireless communication, there is a case that a wireless communication terminal exceeds an electromagnetic wave receivable area from a wireless base station with which it is communicating or that another base station in a better electromagnetic wave receiving state exists. In such a case, a process of switching the base station with which the wireless communication terminal communicates is generated. For example, in case that there are a plurality of candidates as a connection destination base station at the same time, the switching process is generated from a base station with which the wireless communication terminal is connected to another base station, reception electric field intensity from which is stronger than that from the base station when a level of reception signal from the base station (e.g. reception electric field intensity) decreases lower than a predetermined threshold level. The switching process generated at this time is typically referred to as a handover process.
The generation of the handover involves the following situation. Until the wireless communication terminal performs a data communication with a network through the base station, several processes are required such as negotiation for a connection, an authentication process as necessary, and a process of reserving a communication band. For example, there is a case that considerable processes and times are required, depending on a kind of the authentication process. Usually, these processes are required in not only the first connection to the base station but also switching of the base station in the handover. In short, in case of a wireless LAN, when the connection is switched between wireless LAN access points, a considerable connection destination switching time is required. It should be noted that while the connection destination is switched, the data communication is not performed through a newly-connected base station, until the completion of the switching of the connection.
Also, when the wireless communication terminal has two or more wireless communication devices different from each other, there is a case that the network environments are different to which the respective wireless communication apparatuses are connected. For example, one may be a network in which a delay on the network is little and fluctuation in a data transmission interval is null, and the other network may be a network in which a communication band is narrow, the delay is easily generated, and the fluctuation in the data transmission interval is great. At this time, when the switching is performed from one network to the other network (in this description, this switching is also referred to as the handover), the adverse influence on the data communication quality due to the difference in the network environment cannot be avoided. This situation is assumed in a mobile telephone network, a wireless LAN, Bluetooth, NFC, and IEEE 802.16e (WiMAX) whose installation is scheduled in future.
Moreover, even in one wireless interface, there is a possibility that a plurality of candidates of the connection destination network exist. For example, in the wireless LAN, a case that a plurality of wireless LAN access points are found at the same time and one of them is used for connection is considered. Thus, even in this case, there are the many candidates of the connection destination network.
In short, under the situation of the existence of the many wireless interfaces or under the situation of the existence of the many candidates of the connection destination network even in one wireless interface, the situation in which the switching between the communication devices and between the connection destinations is performed, is considered to be increased more and more in future.
If a speech communication or a video reception is performed, when the handover is generated, under the condition that the wireless communication terminal is under any of the foregoing situations, when the quality degradation in the speech communication or discontinuity of reception of the video communication is generated at the timing of the handover. Thus, the lowering of service quality is feared.
Conventionally, the switching of the wireless communication network under the control by the wireless communication terminal is performed at a timing in case of manual switching by a user, or automatically when there is another wireless base station that is connectable at a timing when the lowering of a reception signal level (the received electric field intensity or the like) from the currently connected wireless base station. In this case, the network switching is generated regardless of a communication state of the application being executed currently by the wireless communication terminal, that is, the handover is generated, without respect to the situation that the reception content is not especially desired to be cut. This results in the degradation of the service quality.
For this reason, a technique of controlling the timing of the handover on the basis of the communication state of an application being executed currently is described in Japanese Patent Application Publications (JP-P2001-36936A and JP-P2005-101930A).
In the mobile wireless terminal described in Japanese Patent Application Publication (JP-P2001-36936A), a silence period in speech communication is detected in order to prevent the discontinuity of the speech communication, and a threshold level with respect to a reception signal level (received electric field intensity or the like) is set to be higher than a usual level in the silence period so as to make the handover easier, and reversely, the threshold level is set to the usual level in a non-silence period so as to make the handover difficult.
Also, in the mobile communication terminal described in Japanese Patent Application Publication (JP-P2005-101930A), a handover condition based on a throughput (a reception rate) for each kind of an application is added in addition to the usual handover threshold level based on a communication quality, in order to perform the handover in a suitable period based on the application being executed currently. Specifically, only when a reception signal level representing the level of a reception signal from the base station currently in communication is lower than a preset handover threshold level and the reception rate satisfies a handover condition which is preset to the application.